Does the post show up when you go to posts > posts (the listing) in your dashboard? If so, open it, scroll down below the text area to the "revisions" module and open that module. Your latest autosave and any manual saves should be there and you can then recover one of them. You might not get everything back, but it should bring back most of it.

If it is not in the normal post listing, check the "trash" to see if the post somehow ended up there.